iPhone Shared Album Not Syncing

Hi,

Does anyone know why the Shared Album in my Photos app on three devices is not syncing properly?

Overview:

I have Shared Albums turned on in iCloud for three devices which shows up on my MBP, iPad and iPhone.

1. I can push photos from the iPhone to the MBP and iPad via the Shared Album.
2. I can push photos from the MBP to the iPad, but cannot add to the iPhone's Shared Album.
3. I can push photos from the iPad to the MBP, but cannot add to the iPhone's Shared Album.

So why can I only add to the Shared Album via the iPhone which are sent to other devices, but it cannot receive/fetch photos from other devices to the iPhone?

Solutions I Have Tried:

1. Making sure iCloud Shared Albums is set to ON for all three devices.
2. Making sure that the photos are a standard format such as JPG or PNG.
3. Restarting all three devices.
4. Restarting the WiFi router.
5. Deleting the Shared Album from all three devices and creating a new one.
6. Signing out and then signing back into iCloud on all three devices.

Could this be a bug/issue specific to iOS 17.0.3?

Gear and OS Versions:

1. iPhone 12 Pro
2. iOS 17.0.3
3. MBP M2 Max
4. MacOS 14.0
5. iPad 8
6. iPadOS 17.0.3

Any suggestions or insights are welcome.